Synthesis of erythro-3-pentulose via a pentitol isopropylidene acetal and of l-threo-3-pentulose via a benzylidene acetal of a pentitol

Acetonation of xylitol yielded a mixture of 1,2:4,5-di- O -isopropylidenexylitol (3) and 2,3:4,5-di- O -isopropylidenexylitol ( 4 ). Oxidation of 3 with dimethyl sulfoxide-phosphorus pentaoxide gave ketone 5 , which was hydrolyzed to produce erythro -3-pentulose ( 1 ). The tribenzoate 9 , prepared from 1,3- O -benzylidene- l -arabinitol ( 8 ), was hydrolyzed in acid to yield a mixture of 1,4,5-tri- O -benzoyl- l -arabinitol ( 10 ) and 2,4,5-tri- O -benzoyl- l -arabinitol ( 11 ). Partial benzoylation of 11 , followed by oxidation with dimethyl sulfoxide-phosphorus pentaoxide afforded 1,2,4,5-tetra- O -benzoyl- l - threo -3-pentulose ( 14 ). l - threo -3-Pentulose ( 2 ) was synthesized from 2,4,5-tri- O -acetyl-1,3- O -benzylidene- l -arabinitol ( 18 ). After acid hydrolysis of 18 , the hydrolyzate 19 was partially acetylated to give 20 . Oxidation of the resulting tetraacetate 20 with dimethyl sulfoxide-phosphorus pentaoxide, followed by hydrolysis, yielded 2 . From both 1 and 2 , l-deoxy-(2,4-dinitrophenyl)osazones were obtained that were purified and characterized as the acetates 7 and 23 .